BILLINGS, Mont. (AP) — When a freight train derailed in the Montana town of Culbertson, spilling 27,000 gallons of crude oil, investigators blamed the 2015 accident on defective or missing fasteners used to hold the tracks in place.

The previous year, cracks in a track that went unrepaired caused a train hauling oil to come off the rails and explode along the James River in Lynchburg, Virginia. Broken bolts were cited in another oil train derailment and fire last year in Mosier, Oregon.

Data obtained by The Associated Press shows that tens of thousands of similar safety defects were found when...